Stabilization of image amplifiers



June 20, 1939.v K. SCHLESINGER I STABILIZATION OF IMAGE AMPLIFIERS Filed July I 25, 1936 M a w M Patented June 20, 1939 I UNITED STATES STABILIZATION OF IMAGE AMPLIFIERS Kurt Schlesinger, Berlin, Germany, assignor to Radioaktiengesellschaft D. S. Loewe, Berlin- Steglitz, Germany Application July 23,

1936, Serial No. 92,151

In Germany July 25, 1935 4 Claims.

plify very low frequencies and shows a method used for these amplifiers for preventing effectively the flickering efiect. V

This method will be clearly understood by way of example shown in the accompanying drawing in which there is shown an amplifier circuit for in-g flickering of the anode potential in accordance with the invention.

In this drawing there is shown the diagram of alow-frequency amplifier. I

- The same consists of a photo-cell portion 1, which contains a photo-cell 2 and an initial tube 3, whereby the anode of the cell is connected in direct fashion with the grid of the initial tube 3, all detrimental capacities being avoided. Upon the connection of four amplifying tubes in the casing of the main amplifier 4, output voltages of such phase can be taken at the anode circuit by way of the internal resistance of the rectifier, and primarily, therefore, of the rectifying tube 6, and also the chokes 1, etc., a variation in the anode potential of the feed line 8, and that this variation in the potential of the feed line 8, if its frequency is sufficiently low, is able to pass the feed filters S/Ml and H/IZ and be transmitted by the coupling condensers to a grid of one or more of the earlier tubes of the amplifier. Dependent on the phase of the feed-line fluctuation one or other of the two early stages is able to supply amplified potential, which leads to an initiation of the flickering effect. It is, therefore, impossible to eliminate the flickering effect by a simple reversal of the phase, and it would appear necessary fundamentally to avoid a fluctuation of the anode potential of the feed line 8.

For this purpose there is provided in accordtelevision purposes using a method for preventpowerful current of the final stage 5 produces ance with'the invention a special phase reversing tube l3. The tube 13 is so coupled with'the positive end-stage 5 by means of a potential distributor (see below) that the same is traversed in its anode circuit by currents of the same amplitude but of opposite phase. In other words, the output line I I of the positive end-stage 5 is traversed by a potential which is the same as that in the output line l5 of the negative endstage but is oppositely directed or, shifted in phase to the extent of 180. In this case the connecting point 8 of the two common anode resistances'is a point which is neutralized, in respect of all fluctuations in potential. The currents entering the tube 5 are exactly compensated by the alternating currents leaving the tube I3 so long as the coupling between the tubes 5 and I3 is such as to give unity amplification and 180 phase shift. It may be shown that in the case of a variation in the potentiometer tapping point I i-flickering again occurs to the right: and left of the correct position. On the other hand it is possible to steady the amplifier merely by correct adjustment of the tapping point It. Upon a reduction in the total amplification, which may be performed in one of thepreliminary stages or the couplings between the preliminary stages, the quality of the neutralization is not affected, but merely improved. After the two tubes 5 and 13 have been adapted to each other in the manner described it is possible to provide the filters for the anode current I and 33' and for the grid potential 34 and 35 in common to both tubes, as the condensers 33 and 35 are now safeguarded against fluctuations in potential.

The reversing tube 1-3, in addition to fulfilling the purpose of compensating the flickering effect in accordance with the invention, may also be employed in useful fashion when the transmission of negative films is concerned. A particular stabilizer is no longer necessary in the case of an amplifier'of this character, and it is possible to employ mains-connected apparatus of normal construction or also batteries, even if these possess 'a comparatively high internal resistance.

The coupling between the positive end-stage and the negative end-stage should be effective over the total band to be amplified without phase shift and with constant distribution of potential in reversed amplification ratio. The size of the coupling resistances I! and E8 of this distributor is, therefore, limited in the upward direction by the detrimental capacities which the tubes represent in operation. The capacities are of the order of 0.3- to 0.6-10- microfarads, and the resistances should be at the most equal to the apparent capacitative impedance. In the case of images having approximately 200 lines there reassumed that the tubes 5 and I3 perform approximately two-fold amplification, and that there are anode resistances l9 and 20 of 'approximately LOGO-2,000 ohms.

The potential division between valves 5 and I3 can also be employed to improve the reproduction of the higher frequencies by valve [3. For this purpose a variable condenser 2| is shunted across resistance IT. The impedance of condenser 2| at the high frequencies should be equal to or greater than that of resistance I1, e. g. condenser 2| may be of about 0.6-10- microfarads maximum capacity. The blocking condenser 22 should have an impedance at the lowest pass frequency which is low compared with that of the potential divided ll, l8. For the potential divider values stated, condenser 22 should have a capacity of about 10 mf.

In numerous cases it is desirable to neutralize not only the final stages but also the preliminary stages against detrimental fluctuations of the anode potential line or also of the grid bias, as the grid bias in the case of an amplifier operated wholly from the mains is generated at a bias resistance 23 traversed by the total anode current, and accordingly also in this way a transmission of detrimental potential fluctuations to the preliminary stages is possible and has been found to exist.

' An additional means against flicker resides in the use of a successive anode current filtering separated according to amplifier groups. This method is to be gathered from the drawing, in which the anode current is succesively filtered three times. The first filtering takes place in respect of the end stages and is performed by the chokes and the mains-connection condensers 33. For the three preceding preliminary stages there is provided a second filtering 9/10, wherein the resistance 9, corresponding with the reduced anode current requirement of the preliminary stages, may already be allowed to reach a size of several thousand ohms, and the condenser IO may be of the order of several times 10 mf. A third anode current filtering is'performed by the chain II and I2 in respectof the photocell tube alone. tube is very smallto diminish noise-effective filtering may in this case be performed with 20,000 ohms against 20 mi.

I claim:

1. In an amplifier circuit arrangement for television purposes also for amplifying very low fre--- quencies comprising several amplifier tubes a mains supply circuit for supplying said stages with feed potential and filter-elements in the feed lines of the single amplifiers, an additional amplifier tube provided for applying to the feed lines neutralizing oscillations which are equal in magnitude but opposite in phase to oscillations which would otherwise be fed to said mains supply circuit by said amplifiers, said additional amplifier tube being coupled with its anode via its anode resistance to said mains supply circuit and with its grid via an adjustable potential divider to the anodeof the final tube of said amplifier stage, the anodes of both said tubes being each connected via a condenser to a separate terminal only one of which is used as output terminal.

2. In an amplifier circuit arrangement for television purposes also for amplifying very low frequencies comprising several amplifier tubes a Since the anode current of this 1 mains supply circuit for supplying said stages with feed potential and filter-elements in the feed lines of the single amplifiers, an additional amplifier tube provided for applying to the feed lines neutralizing oscillations which are equal in magnitude but opposite in phase to oscillations which would otherwise be fed to said mains supply circuit by said amplifiers, said additional amplifier tube being coupled with its anode via its anode resistance to said mains supply circuit and with its grid via an adjustable potential divider to the anode of the final tube of said amplifier stage, the anodes of both said tubes being each connected via a condenser to a separate terminal, only one of which is used as output terminal, said potential divider being such as to favour the transmission of the higher frequencies.

3. In an amplifier circuit arrangement for television purposes also for amplif ing very low frequencies comprising several amplifier tubes a mains supply circuit for supplying said stages with feed potential and filter-elements in the feed lines of the single amplifiers, an additional amplifier tube provided for applying to the feed lines neutralizing oscillations which are equal in magnitude but opposite in phase to oscillations which would otherwise be fed to said mains supply circuit by said amplifiers, said additional amplifier tube being coupled with its anode via its anode resistance to'said mains supply circuit and with its grid via an adjustable potential divided to the anode of the final tube of said amplifier stage, the anodes of both said tubes being each connected via a condenser to a separate terminal only one of which is used as output terminal, said potential divider being such as to favour the transmission of the higher fre- 'feed lines of the single amplifiers, which consist of ear-thing condensers in combination withseries resistance being arranged in such a mannerthat the anode current supplied to the earlier valves of said amplifier stage is filtered to a greater eX- tent than that supplied to a later valve of said amplifier stage, an additional amplifier tube provided for applying to the feed lines neutralizing oscillations which are equal in magnitude but opposite in phase to oscillations which would otherwise be fed to said mains supply circuit by one or more of said amplifiers, said additional amplifier tube being coupled with its anode via its anode resistance to said mains supply circuit and with its grid via an adjustable potential divider to the anode of the final tube of said amplifier stage, the anodes of both said tubes being connected via a condenser to a separate terminal only one of which is used as output terminal, said potential divider being such as to favour the transmission of the higher frequencies, a portion of said potential divider at its high potential end being shunted by a condenser whose impedance at high frequencies is equal or greater than that of said portion of the .potential divider.

KURT SCHLESINGER. 

